1. Field of the Invention
This invention relates to a method for treating a catalyst used for catalytic reaction of hydrocarbons when the catalyst is removed from the reaction system.
2. Description of the Prior Art
Generally, in the treatment (e.g., cracking or desulfurization) of hydrocarbons such as gasoline, kerosene or heavy oils in a catalytic reaction, the catalyst used in the reaction must be deactivated, or when the catalyst becomes contaminated, it needs to be removed from the reaction system and exchanged with a fresh catalyst. The previous practice in the removal of the catalyst has been to stop the reaction of a starting hydrocarbon feed oil (to be referred to hereinafter simply as a "feed oil") and removing the feed oil from the reaction system, and to wash the reaction system and the catalyst in the reaction system using a washing oil such as kerosene or a gas oil under appropriately selected temperature and pressure conditions. The catalyst so washed is then removed from the reaction system.
When, for example, a high boiling oil such as an atmospheric residue is used as the feed oil, the spent catalyst exists in a caked state, and therefore, the catalyst cake must be mechanically pulverized. A dust of the pulverized catalyst is generated as a result of, for example, impact at the time of removal, and the dust markedly degrades the working environment. Furthermore, even though the catalyst has been washed in most cases as mentioned above, the spent catalyst removed from the reaction system has adhered thereto, sulfur, iron, vanadium and other metals contained in the feed oil and carbon resulting from the cracking of the hydrocarbons in the feed oil. Accordingly, when the catalyst is removed into the atmosphere, the adhering matter is oxidized by oxygen in the air generating a heat of reaction, which in turn causes the adhering matter on the spent catalyst to burn, resulting in a spontaneous combustion of the spent catalyst. In addition, the sulfur adhering to the spent catalyst generates sulfur dioxide gas by oxidation, and markedly degrades the working environment.
Thus, in the conventional removal of spent or contaminated catalysts for exchange in catalytic reactions of hydrocarbons, the generation of dust, the occurrence of spontaneous combustion and the generation of sulfur dioxide gas causes remarkable difficulties in the removal operation.